1. Field of Invention
This invention pertains to a battery management system for a multi-cell battery system.
2. Description of the Related Art
Portable power sources are becoming ubiquitous. Batteries provide operating power to many portable devices, from handheld devices to electric vehicles. As the portable devices become more powerful and greater demands are placed on them, so too must the power supply be able to provide the power needed by those devices.
Traditionally, batteries were charged as a unit. That is, a single battery charger charged all the cells in their connected configuration. This arrangement, although simple to implement, is inefficient. Typically, the cells in a multi-cell battery do not all have the same state of charge before and after charging. If one cell has a higher state of charge before charging, then that cell may be overcharged by bringing up the other cells to a full charge state. Or, that cell may be fully charged, but the cells that started at a lesser charge state are not fully charged. Either situation is not desirable.
Attempts have been made to provide even charging of battery cells and/or to equalize the charge between cells. For example, Published Application Number 2006/0097700 discloses a battery with most of the series connected cells 320-335 having a charging source 305-315, a shunt regulator 350-360, and a cell monitor 380-395. The charging sources 305-315 are used one at a time with the shunt regulators 350-360 isolating the cells that are not to be charged. U.S. Pat. No. 6,150,795 discloses a single charge source 32 connected to a battery with series connected cells 31. Parallel with the cells 31 are equalizer diverter modules 36 that equalize the charge on the cells 31.
Another example is U.S. Pat. No. 6,369,546, which discloses an array of cell units 12 for an orbiting satellite The cell units 12 are grouped into cells 14 of parallel connected cell units 12. Each group of parallel connected cell units 12 has a charging circuit 26 and a bypass switch 28. A single bulk charger 16 charges all the cells 14 at a high rate and then equalization/balancing is performed by a plurality of balancing switches 22 connected to corresponding transformer/rectifier circuits 26 that provide individual equalization of the cells 14. U.S. Pat. No. 6,586,909 discloses isolated regulators 26 connected to each cell 40 of a battery 30. The charging system uses a multiple-winding transformer 20 to supply regulators 26 connected to the individual cells 40, or group of cells. Each regulator is supplied power from a single winding 22 of the multiple-winding transformer 20.